GB2037982A

GB2037982A - Detection of sodium hydroxide and/or calcium oxide in aerosol form

Info

Publication number: GB2037982A
Application number: GB7943338A
Authority: GB
Original assignee: Draegerwerk AG and Co KGaA
Current assignee: Draegerwerk AG and Co KGaA
Priority date: 1978-12-22
Filing date: 1979-12-17
Publication date: 1980-07-16
Also published as: DE2855648C2; DE2855648B1; SE7909475L; FR2444938A1; SE430630B; GB2037982B; NL7905886A; FR2444938B1; US4259287A; JPS5587044A

Description

1'

GB 2 037 982. A 1

SPECIFICATION

Sodium hydroxide and calcium oxide detection apparatus

This invention relates to a detection apparatus i 5 for detecting the presence of sodium hydroxide and/or calcium oxide in aerosol form in a gas.

Detection apparatus for the quantitative detection of sodium hydroxide or calcium oxide in aerosol form are not hitherto known. The reason 10 for this is that an ill-defined reaction behaviour of the aerosols with the reagents in the detection apparatus normally occurs.

A known method, described in German Patent Specification 742689, for detecting both volatile 15 and misty poisonous arsine substances for use in chemical warfare used a detection tube in which a filter comprising inorganic or organic fibrous material, for example glass wadding, cellulose, asbestos, is placed before a highly active layer of 20 silica gel. When a sample of air is passed through the tube, arsine mist contained therein is retained in the filter, whilst volatile arsines only are absorbed by the silica gel. A reagent which comprises a solution of stannous chloride in 25 concentrated hydrochloric acid, is subsequently introduced into the detection tube. The particles of mist retained by the fibrous filter are carried along by the reagent to the iayer of silica gel. The mist droplets only react with the reagent on the silica 30 gel. Consequently, the reaction in the form of an arsine precipitation always occurs on the layer of silica gel, irrespective of whether arsine mists or volatile compounds are present. The reaction takes place directly between the substances to be 35 detected and the indicating reagent which is introduced. The activity of the silica gel plays an inportant role in the reaction process, and is greatly influenced by the fluid reagent. Therefore this measuring process is only concerned with 40 qualitative detection of the poisonous arsine substances used in chemical warfare.

Furthermore, the use of the fluid reagent solution is not entirely without danger.

According to the present invention there is 45 provided an apparatus suitable for detecting the presence in a gas of sodium hydroxide and/or calcium oxide in the form of an aerosol, the apparatus comprising: a housing having an elongate chamber; a first reagent comprising " 50 ammonium chloride contained in a first zone of the chamber and capable of reacting with sodium hydroxide and/or calcium oxide to release » ammonia; and a second reagent comprising an acid contained in a second zone of the chamber 55 and capable of reacting with ammonia to produce a detectable end product, the first reagent being disposed between the second reagent and one end of the chamber; the apparatus being such that, in use, when a gas with sodium hydroxide 60 and/or calcium oxide entrained therein as an aerosol is introduced into the chamber through said one end of the chamber, the gas passes through the first zone and then through the second zone, the sodium hydroxide and/or calcium

65 oxide in the gas reacting with the ammonium chloride to release ammonia in proportion to the quantity of sodium hydroxide and/or calcium oxide that has reacted with the ammonium chloride, and the ammonium chloride then being conveyed to 70 the second zone and reacting therein with the acid . to produce a detectable end product present in a quantity proportional to the quantity of sodium hydroxide and/or calcium oxide in the gas passed through the chamber.

75 Preferably the ends of the housing are initially closed and the end regions of the housing are relatively weakened so that, in use the end regions of the housing may be broken off in order to open both ends of the housing.

80 The apparatus can also include a variable volume chamber, with that end of the chamber remote from said one end being connected or connectible to said variable volume chamber, whereby, in use, a known quantity of the gas can 85 be drawn through the chamber by expanding the variable volume chamber, thus permitting the second zone to indicate the concentration of sodium hydroxide and/or calcium oxide in the gas.

Preferably the first zone is occupied by a 90 support material impregnated with the first reagent, and the second zone is occupied by a support material impregnated with the second reagent.

The second reagent can comprise an acid and 95 bromophenol blue.

Preferably the housing is a glass tube.

Thus, in a preferred embodiment of the present invention, the detection apparatus has a glass tube with a first zone and a second zone 100 downstream of the first zone inside the glass tube. The first zone is impregnated with a reagent capable reacting with sodium hydroxide and/or calcium oxide in aerosol form. The aerosol is separated out in the first zone under the filtering 105 action of the support material for the first zone. Following separation the sodium hydroxide and/or calcium oxide reacts with the first reagent,

forming a volatile reaction product. The quantity of the first reagent is preferably in excess of any 110 possible quantity of sodium hydroxide or calcium oxide that is drawn into the tube when the reaction is viewed stoichiometrically. The mass of the volative reaction product, which is proportional to the quantity of reaction sodium 115 hydroxide and/or calcium oxide, then flows to the second zone. The volatile reaction product then reacts with the second reagent in the second zone to produce a detactable end product.

The detection apparatus has a simple 120 construction having only two zones and is capable of providing a quantitative measurement of the NaOH and/or CaO aerosols present.

For a better understanding of the present invention and to show more clearly how the 125' same may be carried into effect, reference will now be made, by way of example, to an embodiment of a detection apparatus shown in the accompanying drawing.

The detection apparatus comprises a glass tube

2

GB 2 037 982 A 2

2 in which there is a first zone 1 and a second zone 5. The first zone 1 is occupied by a support material, for example glass fibre on silica gel, impregnated with ammonium chloride. The 5 second zone 5 is similarly occupied by a support material impregnated with acid and bromophenol blue (Tetrabromophenol-sulphon-phthalein). In order to prevent contamination or deterioration of the reagents during storage, the tube 2 can be 10 formed with closed ends which have weakened portions. In use, the ends are snapped off to open the tube 2 and an end of the tube 2 is inserted into a socket of a pump.3. The pump 3 defines a variable volume chamber and by expanding this 15 chamber a known volume of air may be drawn through the tube 2.

In use, a known volume of air is drawn through the tube 2 by the pump 3. Any sodium hydroxide or calcium oxide 4 in the air, or at least sodium 20 hydroxide or calcium oxide in aerosol form, are absorbed or adsorbed in the first zone 1 in which the NaOH and/or CaO react with ammonium chloride to produce ammonia. The gaseous ammonia then flows to the second zone 5 in 25 which one of the components of the second reagent, namely an acid, reacts with the ammonia to produce an ammonium salt. The ammonium salt then reacts with the bromophenol blue to produce a blue region in the second zone 5. The 30 length of this blue region is proportional to the amount of NaOH and CaO that have reacted in the ftrSt zone 1, and is visible through the tube 2. As the volume of air that is drawn through the tube 2 is known, the tube 2 can be marked with a scale 35 indicating the concentration of NaOH and CaO in the air.

The chemical reactions that occur in the tube 2 are:

1) After sorption NaOH and/or CaO in the first 40 zone 1:

NH4CI + NaOH ► NH3+ NaCI + H20

and/or 2NH4CI + CaO »2NH3 + CaCI2 + H20;

and

2) in the second zone 5: 45 bromophenol blue as indicator NH3 + acid >■ammonium salt.

Claims

1. Apparatus, suitable for detecting the 50 presence in a gas of sodium hydroxide and/or calcium oxide in the form of an aerosol, the apparatus conprising: a housing having a elongate chamber; a first reagent comprising ammonium chloride contained in a first zone of the chamber and capable of reacting with sodium hydroxide and/or calcium oxide to release ammonia; and a second reagent comprising an acid contained in second zone of the chamber and capable of reacting with ammonia to produce a detectable end product, the first reagent being disposed between the second reagent and one end of the chamber; the apparatus being such that, in use, when a gas with sodium hydroxide and/or calcium oxide entrained therein as an aerosol is introduced into the chamber through said one end of the chamber, the gas passes through the first zone and then through the second zone, the sodium hydroxide and/or calcium oxide in the gas reacting with the ammonium chloride to release ammonia in proportion to the quantity of sodium hydroxide and/or calcium oxide that has reacted with the ammonium chloride, and the ammonium chloride then being conveyed to the second zone and reacting therein with the acid to produce a detectable end product present in a quantity proportional to the quantity of sodium hydroxide and/or calcium oxide, in the gas passed through the chamber.

2. Apparatus as claimed in claim 1, wherein the ends of said housing are initially closed and the end regions of the housing are relatively weakened so that, in use, the end regions of the housing may be broken off in order to open both ends of the housing.

3. An apparatus as claimed in 1 or 2,. which also includes a variable volume chamber, with that end of the chamber remote from said one end being connected or connectible to said variable volume chamber, whereby, in use, a known quantity of the gas can be drawn through the chamber by expanding the variable volume chamber, thus permitting the second zone to indicate the concentration of sodium hydroxide and/or calcium oxide in the gas.

4. An apparatus as claimed in claim 1, 2 or 3, wherein the first zone is occupied.by a support material impregnated with the first reagent, and the second zone is occupied by a support material impregnated with the second reagent.

5. An apparatus as claimed in any preceding claim 4, wherein the second reagent comprises an acid and bromophenol blue.

6. An apparatus as claimed in any preceding claim, wherein the housing is a glass tube.

7. An apparatus as claimed in claim 1, substantially as hereinbefore described with reference to, and as shown in, the accompanying drawing.

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Printed for Her Majesty's Stationery Office by the Courier Press, Leamington Spa, 1980. Published by the Patent Office, 25 Southampton Buildings, London, WC2A 1 AY, from which copies may be obtained.